linux-kernel - Re: [PATCH 1/3] KVM: SVM: Get rid of handle_fastpath_set_msr

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Message-ID: <CANRm+CxLpGaC66TVUftrxXdfBg+CHJzDMKh4mFvdpm-HTK0QwA@mail.gmail.com>
Date:   Wed, 9 Sep 2020 16:38:37 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, kvm <kvm@...r.kernel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        "Paul K ." <kronenpj@...nenpj.dyndns.org>,
        "# v3 . 10+" <stable@...r.kernel.org>
Subject: Re: [PATCH 1/3] KVM: SVM: Get rid of handle_fastpath_set_msr_irqoff()

On Wed, 9 Sep 2020 at 16:23, Vitaly Kuznetsov <vkuznets@...hat.com> wrote:
>
> Wanpeng Li <kernellwp@...il.com> writes:
>
> > From: Wanpeng Li <wanpengli@...cent.com>
> >
> > Analysis from Sean:
> >
> >  | svm->next_rip is reset in svm_vcpu_run() only after calling
> >  | svm_exit_handlers_fastpath(), which will cause SVM's
> >  | skip_emulated_instruction() to write a stale RIP.
> >
>
> This should only happen when svm->vmcb->control.next_rip is not set by
> hardware as skip_emulated_instruction() itself sets 'svm->next_rip'
> otherwise, right?

The bug is reported here
https://bugzilla.kernel.org/show_bug.cgi?id=209155 , the old machine
which the reporter uses doesn't have NRIP save on #VMEXIT support. :)

    Wanpeng